Understanding of the association between Linux kernel and root file system

Understanding of the association between the Linux kernel and the root file system-Linux general technology-Linux technology and application information. The following is a detailed description. A beginner asks a question. Just give an answer at a glance;
When the system starts, does grub determine the kernel location through its own record information? And pass the boot information to the kernel according to the configuration? The most important thing is the location of the root directory, right?
Then the control is handed over to the kernel. Will the kernel "Mount" the root directory according to the grub information?
Then the kernel is "fixed "? Will Execute inittab to initialize various processes in the system and wait for the user to log on?
Is it our application system?
If the above inference is correct, I compiled a new kernel and changed the grub boot settings. For example, I added a new kernel location in the boot menu, and pass the original root file location to the new kernel. Assuming there is no compatibility problem with the kernel, I will get a new system with the original files unchanged based on the new kernel? Does this mean replacing the kernel with linux advanced technology?
Of course, with my current understanding of the Linux kernel, I cannot compile an available kernel (6) m: B